Long story short, I plugged a 4 pin molex to 4 pin floppy power connector into a fan header on my board. I got my wires all mixed up and made a horrible mistake. I powered on the system, heard a loud pop, and some smoke rolled out. I immediately disconnected the adapter, realized what I had done, panicked, rebooted the system, and...it worked fine. It has been working fine ever since (2-3 days ago). I ran Prime95 for 24 hours to ensure no stability issues, all of my fans work, all of my I/O ports work, and everything else seems to be working fine, with the exception of the fan header that I blew.

So this leads me to the question of what is it that I likely blew? Will it cause issues down the line?

Captain Ned wrote:Looks like a trace on the underside of the mobo arced to to the case. Pull the mobo and look at the back side.

Interesting. Does this mean that a trace is likely burnt and the problem is irreparable? I was thinking that perhaps I simply blew a fuse or a reverse protection diode and it could probably be swapped out...but if I burnt a trace....

If you connected the 4-pin floppy power connector from your power supply to the 4-pin PWM chassis fan controller on your motherboard, you probably fried the fan speed controller chip. For some builds, this may be a non-essential component.

JustAnEngineer wrote:If you connected the 4-pin floppy power connector from your power supply to the 4-pin PWM chassis fan controller on your motherboard, you probably fried the fan speed controller chip. For some builds, this may be a non-essential component.

Well, it doesn't appear to be a vital component, since the board is still functioning, but my concern lies with if it will cause future issues. I'm trying to determined what blew, exactly, and then determine if it will cause issues in the future.

My guess is that you fried a PCB trace on the underside of the motherboard, and (possibly) also the circuit driving that fan header. If everything else still appears to work, then the rest of the mobo is probably unharmed.

If the blown trace is on the underside (outer layer of the PCB) you might be able to resurrect the fan header by soldering a piece of wire to bridge the blown trace, but you've probably got about 50/50 odds that one of the MOSFETs (the little rectangles with 3 terminals) near that burn mark is fried as well.

Edit: Do you recall how the connector was put on the fan header?

The years just pass like trains. I wave, but they don't slow down.-- Steven Wilson

just brew it! wrote:My guess is that you fried a PCB trace on the underside of the motherboard, and (possibly) also the circuit driving that fan header. If everything else still appears to work, then the rest of the mobo is probably unharmed.

If the blown trace is on the underside (outer layer of the PCB) you might be able to resurrect the fan header by soldering a piece of wire to bridge the blown trace, but you've probably got about 50/50 odds that one of the MOSFETs (the little rectangles with 3 terminals) near that burn mark is fried as well.

Edit: Do you recall how the connector was put on the fan header?

It was put on correctly, but it was carrying a 12V current, since it was the molex -> 4 pin connector usually used for floppy drives, but identical to the ones used for fans. This is where my confusion lay when I was plugging things in and I had a major brain fart. So basically I fed a pure 12V current into the circuit that the fan header was on.

Floppy connectors have 4 wires, that fan connector has 3. Where was the extra pin of the Molex - above the fan connector or below it? (If you remember...)

Edit: I really wish they would key the connectors such that this kind of mistake is impossible. In similar fashion, you can also plug a PCIe GPU power plug into the motherboard ATX12V power jack. This has the effect of bridging the +12V rail to groound. Not good. (And yes, been there done that... )

The years just pass like trains. I wave, but they don't slow down.-- Steven Wilson

just brew it! wrote:Edit: I really wish they would key the connectors such that this kind of mistake is impossible.

Don't get me started, ATX standards have been around for how long and they still supply you with a bunch of individual PITA pins to plug in Power,HD LED,Reset,Power LED and speaker? $%^$%#! that annoys me, just give me a damn keyed plug already.

Mmm, this reminds me of that one time I hooked up a floppy drive but was off by one pin and got a fun surprise when flipping the switch. I still use that PSU, though one of the two floppy plugs and part of the drive melted into goo. Real champ, that power supply. I miss having an A:\ drive and emorage a little bit every time I see a motherboard that won't support a floppy--which is all of them these days--but I don't miss that crappy power plug.

Murderbydeath wrote:If I'm reading the pinouts correctly, ground was going into ground, ground into +12V, and +12V into tachometric signal (I'm guessing the RPM signal), if that helps.

Yup. The trace that blew was almost certainly the one supplying +12V to the header, since it was basically shorted to ground. The tach sensor input may or may not have survived, depending on how it is designed.

The years just pass like trains. I wave, but they don't slow down.-- Steven Wilson

I had something come up and I'm out of town for the weekend, but I'll flip the board over, clean off any burns, and take some pictures as soon as I'm back. Might be tonight or tomorrow. Thanks for all the help, guys. Most knowledgeable people I've encountered about this issue (I've posted in like 6 different places).

You do have the brass standoff's on the motherboard tray?? I ask this because the motherboard looks like it is laying right on the motherboard tray in the photo. That could make bad things happen if the motherboard is just screwed to the tray with no standoffs to electrically insulate the back of the board.

vargis14 wrote:You do have the brass standoff's on the motherboard tray?? I ask this because the motherboard looks like it is laying right on the motherboard tray in the photo. That could make bad things happen if the motherboard is just screwed to the tray with no standoffs to electrically insulate the back of the board.

Didn't catch that the first time around assuming that anyone would have the standoffs in place.

He has erected a multitude of New Offices, and sent hither swarms of Officers to harass our people and eat out their substance.

vargis14 wrote:You do have the brass standoff's on the motherboard tray?? I ask this because the motherboard looks like it is laying right on the motherboard tray in the photo. That could make bad things happen if the motherboard is just screwed to the tray with no standoffs to electrically insulate the back of the board.

Of course. This isn't the first PC I've built, just the first I've built and done something this silly.

I would be assuming that a resistor has popped - that's the obvious result of voltage through a circuit that isn't expecting any - and resistors do go "pop" and release quite a lot of smoke when they are overfed.Most IC is protected by diodes too - so there's a large chance that everything apart from the fan header itself is still okay.

Obviously assumptions and chance aren't exactly cast-iron answers but I'd just keep on using it for the moment, avoiding that particular fan-header in future.

Some people ask me why I have always enclosed my signature in spoiler tags; There is a good reason for that, but I can't elaborate without giving away the plot twist.

If that header lacks fan speed control (note: some 3-pin headers do have it even though they lack the PWM pin), the +12V pin is probably just wired directly to the +12V power plane (no resistor or other component in between). Most motherboard components also tend to be on the top side of the PCB not the bottom (though exceptions do exist).

The years just pass like trains. I wave, but they don't slow down.-- Steven Wilson

I'm thinking it's possible that the Q15 triode (I assume that's a MOSFET -- it IS a SOT-23 transistor, isn't it?) blew, or the D7 diode blew. The D7 diode does look a little jarred in that picture, doesn't it? I'll PROBABLY take those pictures tonight, sorry for all the delays.

I suppose I could easily test if it was the D7 diode, as long as I were careful. Plug a fan in, power on the board, take a wire and jump the diode pin to where the trace goes. But I'm afraid I'd end up shorting something else out, haha.

Last edited by Murderbydeath on Tue May 14, 2013 4:48 pm, edited 2 times in total.

The location of the burn mark seems more consistent with a trace (or component, if there are any there) on the underside of the PCB burning up. If Q15 or D7 was responsible I would expect to see some discoloration of the silkscreened white lettering and graphics on the top side of the PCB.

The years just pass like trains. I wave, but they don't slow down.-- Steven Wilson

Alright guys, I took some pictures, but...none of them turned out that great. I couldn't get good lighting or the camera to focus, but I want you to know that you were right: it was a burnt trace. The unfortunate thing is that it seems to have burned an adjacent trace along with it. The trace that burned was actually 2 traces that were very close to each other; there's no telling if both were damaged or just one. It looks like both. There was also an adjacent trace that looks like it might have taken some damage. But I can't be sure. The damage is done, though, right? There won't be any issues down the line as a result of this...right?

There are also a couple of pictures of the back of my CPU mounting plate. Or whatever that thing is. It had some dark marks on it. They look kind of like burns. I find that concerning. But my CPU temps are always fine.

Edit: Wow yeah these pictures are garbage. Basically the trace at the very top of the board is actually 2 small traces. They both looked pretty damaged, as well as probably the trace below them. I'm not sure where any of them go.

I really apologize for the poor quality of these pictures. I seriously could not get my camera to focus. And I was nervous about having the board in my hands while taking pictures (I really didn't want to take the HSF off)

just brew it! wrote:Couldn't tell much from the pics, too blurry. Sorry.

Still, knowing now that it's a trace, you can say if the damage is done or if it will perhaps cause issues that will worsen over time, right? I assume that the damage is done and that no more than what is already damaged will happen, but I could be wrong.

Well, can't say for certain because there could still be latent damage to some other component. But odds are, yeah the damage is done and anything that is still working now will be unaffected in the future.

The years just pass like trains. I wave, but they don't slow down.-- Steven Wilson